Under normal conditions, inflammation is a process that helps an animal recover from injury. Acute inflammation is the initial response of a tissue to harmful stimuli. It involves a complex, highly regulated process that begins when cells present in the injured tissue, including macrophages, dendritic cells, histiocytes, Kupffer cells, and mastocytes, sense molecules associated with the injury and become activated. Upon activation, these cells release inflammatory mediators, such as vasodilators. The vasodilators induce increased blood flow and permeability of the blood vessels in the vicinity of the injury. This, in turn, results in the increased movement of plasma and leukocytes (including neutrophils and macrophages) from the blood into the injured tissue. Because inflammatory mediators are, in general, rapidly degraded, acute inflammation requires constant stimulation in order to be sustained. As a result, acute inflammation ends once the harmful stimulus is removed.
Various agents, including but not limited to bacteria, viruses, physical injury, chemical injury, cancer, chemotherapy, and radiation therapy, can, depending on the specific agent and the genetic makeup of the animal exposed to it, cause prolonged and excessive inflammation. Such inflammation, known as chronic inflammation, is believed to be a contributing factor to many widespread and debilitating diseases, including heart disease, cancer, respiratory disease, stroke, neurological diseases such as Alzheimer's disease, diabetes, and kidney disease. The result of chronic inflammation is the destruction of normal tissue and its replacement with collagen-rich connective tissue. Collagen-rich connective tissue, also known as scar tissue, exhibits diminished tissue function as compared to normal tissue. Persistent and prolonged formation of scar tissue, in turn, leads to fibrosis. Fibrosis is among the common symptoms of diseases affecting the lungs, skin, liver, heart, and bone marrow, and is a critical factor in diseases such as idiopathic pulmonary fibrosis, scleroderma, keloids, liver cirrhosis, myocardial fibrosis, diabetic kidney disease, myelodysplastic syndrome, and other disorders.
Studies of chronic inflammation and fibrosis have indicated that, regardless of the activating agent and the tissue affected, a common network of signaling proteins tend to function together to establish the pro-inflammatory state. This network of signaling proteins includes a number of different cytokines, cytokine receptors, transcription factors, and micro RNAs, including TGFβ, TGFβRII, and miRNA19b.
Despite growing knowledge about conditions that involve excessive inflammation, such as chronic inflammation and fibrosis, treatments for such conditions remain elusive. Many drugs and other substances have been shown to have anti-inflammatory activity, either in vitro or in vivo, but for many indications caused or potentiated by inflammation, there are still no therapies. In addition, many anti-inflammatory therapies are associated with harmful side effects. Thus, there remains a critical need to identify therapeutic agents that reduce inflammation without harmful side effects.